Free radical polymerisation process

ABSTRACT

Process for the free-radical polymerisation of olefinically unsaturated monomer(s) using a free-radical initiator, wherein said polymerisation is performed in the presence of a compound for effecting molecular weight control, said molecular weight control compound being selected from Cobalt II chelates of the following formulae I, II and III: ##STR1## wherein: x and y are independently 2 to 5; 
     each R 1 , R 2 , R 3  and R 4  is independently selected from H, C1-C12 alkyl, optionally substituted aryl, OR 5  where R 5  is C1 to C12 alkyl or optionally substituted aryl, CO 2  R 5 , SO 3  H, C(═O)R 5 , CO 2  H, NO 2 , OH, NR 5   2 , NH 2 , NHR 5 , SR 5 , SH, CN, SO 3  R 5 , halogen, 2-furyl and 3-furyl; 
     each X is independently selected from (CR 6   2 ) n , (CR 6   2  O) n , optionally substituted o-phenylene, and optionally substituted 1,8-naphthylene, where each R 6  is independently selected from H and C1 to C12 alkyl, and n is 1 to 10; 
     and wherein said cobalt chelates of formulae I and II possess a positive charge of 2 and are associated with an anion or anions for balancing the positive charge, while that of formula III is neutral; 
     and also Co III analogues of said cobalt II chelates of formulae I, II and III in which the Co atom is additionally covalently bonded, in a direction at right angles to the macrocyclic chelate ring system, to H, a halide ion or other anion, or a homolytically dissociatable organic group.

This application claims benefit of international application PCT/GB94/01693, filed Aug. 2, 1994.

The present invention relates to a process for the free-radicalinitiated polymerisation of olefinically unsaturated monomer(s) in whichmolecular weight control is achieved by the presence of certain cobaltchelate complexes.

Polymers of low molecular weight, known as oligomers, are often desiredfor various applications (such as coating compositions) either in theirown right or as precursors for other polymers. In order to formoligomers it is necessary to appropriately control the polymerisationprocess being used to yield the desired type of product. In free-radicalpolymerisations, which are widely used for polymerising olefinicallyunsaturated monomers, various conventional means are employed forcontrolling and limiting the molecular weight of the growing polymerchains. Of these, the addition of thiol compounds to the polymerisationhas probably been used the most extensively; the thiol acts as aneffective chain transfer agent but unfortunately contaminates the systemto which it has been added by virtue of its distinctive and persistentodour.

More recently, attention has turned to the use of various transitionmetal complexes, particularly cobalt chelate complexes, as chaintransfer agents for use in controlling molecular weight when radicallypolymerising olefinically unsaturated monomers.

For example, various literature references, such as N. S. Enikolopyan etal, J. Polym. Sci., Polym. Chem. Ed., Vol 19, 879 (1981), disclose theuse of cobalt II porphyrin complexes as chain transfer agents in freeradical polymerisation, while U.S. Pat. No. 4,526,945 discloses the useof dioxime complexes of cobalt II for such a purpose. Various otherpublications, e.g. U.S. Pat. No. 4,680,354, EP-A-0196783, andEP-A-0199436, describe the use of certain other types of cobalt IIchelates as chain transfer agents for the production of oligomers ofolefinically unsaturated monomers by free-radical polymerisation.WO-A-87/03605 on the other hand claims the use of certain cobalt IIIchelate complexes for such a purpose.

We have now discovered that molecular weight control in the free-radicalpolymerisation of olefinically unsaturated monomers may be effectivelyachieved with a further class of cobalt chelate complexes which have notbeen disclosed in the prior art for such use.

According to the present invention there is provided a process for thefree-radical polymerisation of olefinically unsaturated monomer(s)(especially methacrylate monomer(s)) using a free-radical initiator,wherein said polymerisation is performed in the presence of a compoundfor effecting molecular weight control, said molecular weight controlcompound being selected from cobalt II chelates of the followingformulae I, II and III: ##STR2## wherein: x and y are independently 2 to50; each R¹, R², R³ and R⁴ is independently selected from H, C1-C12alkyl, optionally substituted aryl (preferably optionally substitutedphenyl), OR⁵ where R⁵ is C1 to C12 alkyl or optionally substituted aryl(preferably optionally substituted phenyl), CO₂ R⁵, SO₃ H, C(═O)R⁵, CO₂H, NO₂, OH, NR⁵ ₂, NH₂, NHR⁵, SR⁵, SH, CN, SO₃ R⁵, halogen (preferablyC1, Br, I or F), 2-furyl and 3-furyl;

each X is independently selected from (CR⁶ ₂)_(n), (CR⁶ ₂ O)_(n),optionally substituted o-phenylene, and optionally substituted1,8-naphthylene, where each R⁶ is independently selected from H and C1to C12 alkyl, and n is 1 to 10;

and wherein said cobalt chelates of formulae I and II possess a positivecharge of 2 and are associated with an anion or anions for balancing thepositive charge, while that of formula III is neutral;

and also Co III analogues of said cobalt II chelates of formulae I, IIand III in which the Co atom is additionally covalently bonded, in adirection at right angles to the macrocyclic chelate ring system, to H,a halide ion (e.g. Cl⁻) or other anion, or a homolytically dissociatableorganic group.

It is to be understood that, as defined above, the defined cobaltchelates of formulae I and II are positively charged (of charge 2) andare associated with an appropriate anion(s) to balance the positivecharge. Suitable singly charged anions include NO₃ ⁻, C1⁻, Br⁻, N₃ ⁻,CN⁻, OH⁻, C₂ O₄ ⁻, I⁻, BF₄ ⁻, PF₆ ⁻, SbF₆ ⁻, ClO₄ ⁻, NCS⁻ and R⁷ CO₂ ⁻where R⁷ is C1 to C8 alky and two such ions would be associated with agiven cobalt chelate molecule. Br⁻ is a particularly suitable anion.Doubly charged anions such as SO₄ ²⁻ could also e.g. be used (only oneanion being required to balance the positive double charge).

Preferably:

R¹ is selected from H, C1-C12 alkyl and optionally substituted phenyl;R² is selected from H, C1-C12 alkyl and optionally substituted phenyl;R³ is selected from H and C1 to C12 alkyl; and R⁴ is selected from H andC1 to C12 alkyl.

More preferably:

R¹ is selected from H and CH₃ ; R² is H; X is selected from (CH₂)₂ ando-phenylene; R³ is selected from H and CH₃ ; R⁴ is selected from H andCH₃, and x=y=2 or 3 or x=3 and y=4.

A specific example of a Co chelate of formula III is where each R¹ =H,each R² =H and each X is (CH₂)₂, i.e. ##STR3## and another example of aCo chelate of formula III is where each R¹ =H, each R² =H and each X iso-phenylene i.e. ##STR4##

A further example of a cobalt chelate of formula III is where each R¹ =Heach R² =H, the bottom X is CH₂ CH₂ and the top X is o-phenylene, i.e.##STR5##

A particularly preferred example is that of formula I where each R¹ =CH₃; each R² =H, each R³ =H, x=y=3, and R⁴ =H, and the charge balancingcounterion is usually Br⁻, but may be, for example, an acetate,thiocyanate, nitrate or iodide ion as in ##STR6## where Y is Br, CH₃CO₂, SCN, NO₃ or I.

This catalyst is particularly useful as it is soluble in water andaqueous media and is very effective in both emulsion and solutionpolymerisation (see later); also its activity appears to be enhanced inthe presence of carboxylic acid-containing monomers (such as acrylic andmethacrylic acid).

With respect to the various alkyl groups defined supra, they may bestraight chained or branched where the option arises.

With regard to the CoIII analogues of said compounds, these arise whenthe Co is additionally bonded to a further atom, ion or organic groupwhich is homolytically dissociable, such as H, optionally substitutedalkyl, cyano, halide, ester, aryl (including heterocyclic aryl), andalicyclyl (including heterocyclic alicyclyl) such a further group ofnecessity being located in an axial position (i.e. perpendicular to theequatorial ligands as shown in the formulae I to VII). Alkyl groupsbearing one or more substituents on the carbon atom bonded to the metalion are particularly suitable; such substituents may include nitrile,ester, and optionally substituted aromatic groups. Some of these CoIIIcomplexes may be stable materials under ordinary storage conditions, andmay only react under the free-radical-generating conditions of thepolymerisation process. Others, particularly where H is the further(axial) group, may be highly reactive intermediate species--and indeedit is possible that all the CoII complexes (and possibly the CoIII onesas well) exert their chain transfer effect by proceeding through thereactive CoIIIH intermediate. It is also possible that there is always aperiodic interchange between the CoII and CoIII valency states in thecomplexes during the polymerisation. In fact the actual mechanism ofinvolvement is complicated and not properly understood on our part andwe do not wish to be bound by any particular theory nor to anidentification of the specific chemical constitution or valency state ofthe Co complex during the actual polymerisation process.

It is also possible for the cobalt complexes as defined supra (i.e. CoIIor CoIII complexes)to additionally have further ligands coordinated tothe Co atom (presumably axially), which do not alter the Co valencystate. These may be derived en passant from the reaction medium used inthe preparation of the Co complex or from the polymerisation medium usedin the polymerisation process, or may be derived by deliberately addinga compound which will provide such ligands, and it is often the casethat the coordinated presence thereof in the complex will ameliorate thelatter's effectiveness. However, they are not essential to theinvention, and for convenience they have not been shown in the formulaeI to VII. Typical of such additional ligands are weakly basic tertiaryamines such as pyridine (or their substituted derivatives), trialkylamines, dialkylamines, ethers such as tetrahydrofuran and diethyl ether,and also optionally substituted trialkyl, triaryl or tri(alkyl/aryl)phosiphines (or analogous compounds such as corresponding alkoxy oraryloxy phosphines). One or more water molecules could also becoordinated to the Co complex.

The defined cobalt chelate complexes allow the efficient production ofoligomers and could be functioning as catalytic chain transfer agents.Generally speaking, the degree of polymerisation of such oligomers(overall in the case of copolymers) will usually be within the range 2to about 1000 (i.e. 2 to 1000 polymerised units), preferably 10 to 750,and more preferably 10 to 130.

The polymerisation process can be carried out in the presence of apolymerisation medium (acting as a carrier medium for the components andas a heat transfer medium) or in the absence of such a medium (i.e. inbulk). When using a polymerisation medium, the polymerisation may bee.g. a solution, suspension or emulsion polymerisation.

Typical organic solvents which may be used as the medium for a solutionpolymerisation include aromatic hydrocarbons such as benzene, toluene,and the xylenes; ethers such as diethyl ether, tetrahydrofuran,alkoxylated ethylene glycol or polyethyleneglycol; alcohols such asmethanol, ethanol, propanol and butanol and their esters with carboxylicacids such as acetic, propionic and butyric acids; ketones such asacetone or methyl ethyl ketone; and liquid tertiary amines such aspyridine. Mixtures of solvents may be used. Water may also be used as apolymerisation medium, (sometimes in combination with a solvent(s) suchas described above) as in suspension or emulsion polymerisations, andfor such processes conventional emulsifying or suspension agents may beemployed. When emulsion polymerisation is used, as emulsifiers there maybe used anionic surfactants such as the Na, K and ammonium salts ofdialkylsulphosuccinates, Na, K and ammonium salts of sulphated oils, Na,K and NH₄ salts of alkyl sulphonic acids, Na, K and ammonium alkylsulphates (such as Na, K and ammonium lauryl sulphate) and Na, K and NH₄salts of fatty acids. However, cationic emulsifiers such ashexadecyltrimethyl ammonium bromide may also be used. The amount used isusually 0.2 to 15% by weight, preferably 0.2 to 5% by weight based onthe total monomer(s) charged. The polymerisations are usually performedat a temperature within the range of 25° to 160° C. (more usually 45° to110° C.). Any suitable free radical yielding initiator may be used inthe process of the invention, the usual criteria being that it hasacceptable solubility in one or more of the other polymerisationcomponents (e.g. organic solvent, monomers, or water), is sufficientlyactive at the polymerisation temperature (usually having a half lifewithin the range 0.5 to 5 hours), and does not unacceptably affect thestability of the Co chelate. Thus, the initiator may be selected fromsuch free-radical-yielding initiators which may include azo compounds as2,2'-azobis(isobutyronitrile),2,2'-azobis-(2-methyl)butanenitrile,4,4'-azobis(4-cyanovaleric acid),2-(t-butylazo)-2-cyanopropane,2,2'-azobis[2-methyl-N-(1,1)-bis(hydroxymethyl)-2-hydroxyethyl]-propionamide, and 2,2'-azobis[2-methyl-N-hydroxyethyl)]-propionamide.Other soluble free radical initiators may also be used, examples ofwhich may include peroxy compounds such as benzoyl peroxide, lauroylperoxide, hydrogen peroxide, and Na, K, and NH₄ persulphates. Redoxinitiator system can also be used, examples of which include redox pairssuch as NH₄ persulphate and Na metabisulphite.

The process may be carried out using an "all-in-one" batch process inwhich all components are present in the reaction medium at the start ofpolymerisation or a semi batch process in which one or more of thecomponents employed (usually at least one of the monomers) is wholly orpartially fed to the polymerisation medium during the polymerisation.The monomer(s) can be fed neat or as emulsions in water. When more thanone monomer is being added, the composition of the monomer feed in thesemi-batch process may be varied during the feed operation as is wellknown in the art.

The chelates used in the process may be prepared beforehand or may beformed in-situ from the appropriate reactants. Typically, the level ofthe cobalt chelate used in the polymerisation process will be such thatthe ratio of monomer(s)/initiator(molar basis) is within the range offrom 20 to 500, more usually 40 to 300. Also typically, the level ofcobalt employed will be such that the ratio of cobalt chelate tofree-radical initiator(molar basis) is within the range of 0.001 to 0.1,more usually 0.003 to 0.08.

The process of the invention is most effectively applied to the homo-orcopolymerisation of methacrylate esters or styrenes, although acrylateesters can be polymerised, particularly if included as comonomers.

Examples of monomers that may be polymerised include methylmethacrylate, ethyl methacrylate, propyl methacrylate (all isomers),butyl methacrylate (all isomers), and other alkyl methacrylates;corresponding acrylates; also functionalised methacrylates and acrylatesincluding glycidyl methacrylate, trimethoxysilyl propyl methacrylate,allyl methacrylate, hydroxyethyl methacrylate, hydroxypropylmethacrylate, dialkylaminoalkyl methacrylates; fluoroalkyl (meth)acrylates; methacrylic acid, acrylic acid; fumaric acid (and esters),itaconic acid (and esters), maleic anhydride; styrene, α-methyl styrene;vinyl halides such as vinyl chloride and vinyl fluoride; acrylonitrile,methacrylonitrile; vinylidene halides of formula CH₂ ═C(Hal)₂ where eachhalogen is independently C1 or F; optionally substituted butadienes ofthe formula CH₂ ═C(R⁸) C(R⁸)═CH₂ where R⁸ is independently H, C1 to C10alkyl, C1, or F; sulphonic acids or derivatives thereof of formula CH₂═CHSO₂ OM wherein M is Na, K, Li, N(R⁹)₄, R⁹, or --(CH₂)₂ --D where eachR⁹ is independently H or C1 or C10 alkyl, D is CO₂ Z, OH, N(R⁹) or SO₂OZ and Z is H, Li, Na, K or N(R⁹)₄ ; acrylamide or derivatives thereofof formula CH₂ ═CHCON(R⁹)₂, and methacrylamide or derivates thereof offormula CH₂ ═C(CH₃)CON(R⁹)₂. Mixtures of such monomers may be used.

Preferred monomers are C1-C10 alkyl methacrylates, C1-C10 alkylacrylates, methacrylic acid, styrene and styrene derivatives.

The present invention is now illustrated but in no way limited byreference to the following examples. Unless otherwise specified allparts, percentages and ratios are on a weight basis.

GENERAL PROCEDURES Solution Polymerisation

To a 200 ml Schlenk tube filled with dry nitrogen and 0.085 g 2,2'azobis(isobutyronitrile) (AIBN) were added 10 ml methyl methacrylate(MMA) and 20 ml of the appropriate solvent, both of which had beenpreviously sparged with dry nitrogen. The desired amount of cobaltcatalyst was then added and the tube heated at 60° C. for 6 hours undernitrogen. Gel Permeation Chromatography (GPC) was used to determine themolecular weight of the polymer produced against polymethyl methacrylate(PMMA) calibration standards.

Emulsion Polymerisation

0.5 g sodium lauryl sulphate (SLS) were added to a reaction flask fittedwith a dropping funnel and overhead stirrer, the apparatus being filledwith dry nitrogen and immersed in a water bath at 75° C. 80 ml degasseddistilled water and 0.5 g 4,4'-azobis (cyanovaleric acid) (CVA) werethen added. The dropping funnel was charged with 0.5 g SLS, 25 mldegassed distilled water, the desired amount of cobalt catalyst and 50ml degassed methyl methacrylate. The feed, which was continuouslyagitated, was then added to the charge over a period of 2 hours whilestirring the reaction mixture at 170 rpm and the reaction maintained at75° C. for a further 5 hours. A nitrogen atmosphere was maintained inthe flask throughout the reaction. Gel Permeation Chromatography (GPC)was used to determine the molecular weight of the polymer latex producedagainst PMMA calibration standards.

In the following examples, [Monomer]/[Co] means the mole ratio of themonomer or monomers to Co catalyst. MeOH means methanol. Mn is thenumber average molecular weight. Mw is the weight average molecularweight.

EXAMPLES 1-3

These examples illustrate the use of2,12-Dimethyl-3,7,11,17,-tetraazabicyclo [11.3.1]heptadeca1(17),2,11,13,15-pentaene cobalt (II) bromide monohydrate (Co-pydiene),the Co chelate of formula VII (not showing the water ligand), where Y isBr, as a catalytic chain transfer agent in the solution polymerisationof MMA.

The title compound was prepared from the reaction of diacetyl pyridinewith 3,3' diaminodipropylamine in the presence of cobalt bromide asdecribed by D. H. Busch and K. M. Long in Inorganic Chemistry 9(3)(1970)511. The general procedure for solution polymerisation wasfollowed using the indicated amount of Co-pydiene and the results areshown below:

    ______________________________________                                        Example Solvent  [Monomer]/[Co]                                                                              Mn    Mw/Mn                                    ______________________________________                                        1       MeOH     100000        13160 2.5                                      2       MeOH     50000         7740  2.8                                      3       MeOH     10000         1480  1.8                                      ______________________________________                                    

A repeat of the above experiment with no catalyst gave a polymer withMn=51800, Mw/Mn=2.5.

EXAMPLE 4

This example illustrates the use of Co-pydiene as a catalytic chaintransfer agent in the emulsion polymerisation of MMA.

The general procedure for emulsion polymerisation was followed using theindicated amount of Co-pydiene as catalyst (prepared as in Example 1).The results are indicated below:

    ______________________________________                                        Example  [Monomer]/[Co]  Mn      Mw/Mn                                        ______________________________________                                        4        2000            11100   1.7                                          ______________________________________                                    

EXAMPLE 5

This example illustrates the use of Co-pydiene as a catalytic chaintransfer agent in the emulsion copolymerisation of MMA and methacrylicacid (MAA).

The general procedure for emulsion polymerisation was followed exceptthat 48 ml degassed MMA and 5 ml degassed MAA were used instead of MMAalone, using the indicated amount of Co-pydiene prepared as in Example 1as catalyst. The results are indicated below:

    ______________________________________                                        Example  [Monomer]/[Co]  Mn     Mw/Mn                                         ______________________________________                                        5        2000            2630   1.7                                           ______________________________________                                    

A repeat of the above experiment with no catalyst gave a polymer withMn>274000, Mw/Mn>1.8.

EXAMPLES 6-8

These examples illustrate the use of1,5,8,12-tetra-aza-3,4:9,10:13,14-tribenzocyclotetradecane-1, 11-dienatocobalt (II) (Cocyphen), the Co chelate of formula VI, as a catalyticchain transfer agent in the solution polymerisation of MMA.

The title compound was prepared from o-phenylene diamine and4,7-diaza-2,3:8, 9-dibenzodecane-1,10-dione in refluxing methanol in thepresence of cobalt acetate, as described by Tasker and Green in Inor.Chim. Acta (1971) 5.65.

The general procedure for solution polymerisation was followed. Resultswere as indicated below:

    ______________________________________                                        Example  [Monomer]/[Co]  Mn      Mw/Mn                                        ______________________________________                                        6        53085           31600   2.6                                          7        26540           3233    2.2                                          8         9290           1000    1.7                                          ______________________________________                                    

A repeat of the above experiment with no catalyst gave a polymer withMn=47400, Mw/Mn=2.7.

EXAMPLE 9

This example illustrates the use of Co-pydiene in the emulsionterpolymerisation of MMA, MAA and styrene (composition 40/30/30 byweight respectively).

The general procedure for emulsion polymerisation was followed, usingthe amount of catalyst indicated below. The results are also indicated.

    ______________________________________                                        Example  [Monomer]/[Co]  Mn     Mw/Mn                                         ______________________________________                                        9        2000            7970   2.3                                           ______________________________________                                    

EXAMPLE 10

This example illustrates the use of2,12-dimethyl-3,7,11,17-tetraazabicyclo-[11.3.1]heptadeca-1,(17),2,11,13,15-Pentaenecobalt (II) thiocyanate as a catalytic chain transfer agent in thesolution polymerisation of methyl methacrylate (MMA).

The title compound was prepared in an analogous manner to that for thepreparation of Co-pydiene from the reaction of diacetyl pyridine with3,3'-diamino-dipropylamine in the presence of cobalt (II) thiocyanate.The general procedure for solution polymerisation was followed using theindicated amount of the title compound and the results were as shownbelow (molecular weights were measured after 1 hour reaction time).

    ______________________________________                                        Example  Solvent  [MMA]/[Co]   Mn   Mw/Mn                                     ______________________________________                                        10a      MeOH     100,000      6,079                                                                              1.88                                      10b      MeOH     50,000       3,984                                                                              1.56                                      10c      MeOH     10,000       1,103                                                                              1.28                                      ______________________________________                                    

A repeat of the above experiment with no catalyst gave a polymer withMn=60370, Mw/Mn=1.95.

EXAMPLE 11

This example illustrates the use of2,12-dimethyl-3,7,11,17-tetraazabicyclo-[11.3.1]heptadeca-1,(17),2,11,13,15-pentaenecobalt (II) acetate as a catalytic chain transfer agent in the solutionpolymerisation of methyl methacrylate (MMA).

The title compound was prepared in an analogous manner to that for thepreparation of Co-pydiene from the reaction of diacetyl pyridine with3,3'-diamino-dipropylamine in the presence of cobalt (II) acetate andrecrystallised from dichloromethane. The general procedure for solutionpolymerisation was followed using the indicated amount of the titlecompound and the results were as shown below (molecular weights weremeasured after 1 hour reaction time).

    ______________________________________                                        Example  Solvent  [MMA]/[Co]   Mn   Mw/Mn                                     ______________________________________                                        11a      MeOH     100,000      4,605                                                                              1.81                                      11b      MeOH     50,000       4,931                                                                              1.71                                      11c      MeOH     10,000       1,523                                                                              1.74                                      ______________________________________                                    

A repeat of the above experiment with no catalyst gave a polymer withMn=30390, Mw/Mn=2.67.

EXAMPLE 12

This example illustrates the use of2,10-dimethyl-3,6,9,15-tetraazabicyclo-[9.3.1]pentadeca-1,(15),2,9,11,13-pentaene cobalt (II) bromide as a catalytic chaintransfer agent in the solution polymerisation of methyl methacrylate(MMA).

The title compound was prepared in an analogous manner to that for thepreparation of Co-pydiene from the reaction of diacetyl pyridine withdiethylene triamine in the presence of cobalt (II) bromide. The generalprocedure for solution polymerisation was followed using the indicatedamount of the title compound and the results were as shown below(molecular weights were measured after 1 hour reaction time)

    ______________________________________                                        Example Solvent  [MMA]/[Co]   Mn    Mw/Mn                                     ______________________________________                                        12a     MeOH     100,000      55,810                                                                              1.97                                      12B     MeOH     50,000       50,940                                                                              2.02                                      12c     MeOH     10,000       38,780                                                                              1.99                                      ______________________________________                                    

A repeat of the above experiment with no catalyst gave a polymer withMn=55500, Mw/Mn=1.96.

EXAMPLE 13

This example illustrates the use of2,11-dimethyl-3,6,10,16-tetraazabicyclo-[10.3.1]hexadeca-1,(16),2,10,12,14-pentaenecobalt (II) bromide as a catalytic chain transfer agent in the solutionpolymerisation of methyl methacrylate (MMA).

The title compound was prepared in an analogous manner to that for thepreparation of Co-pydiene from the reaction of diacetyl pyridine withN-(2-aminoethyl)-1, 3-propanediamine in the presence of cobalt (II)bromide. The general procedure for solution polymerisation was followedusing the indicated amount of the title compound and the results were asshown below (molecular weights were measured after 1 hour reactiontime).

    ______________________________________                                        Example Solvent  [MMA]/[Co]   Mn    Mw/Mn                                     ______________________________________                                        13a     MeOH     100,000      46,580                                                                              1.96                                      13b     MeOH     50,000       22,710                                                                              2.09                                      13c     MeOH     10,000        8,150                                                                              2.35                                      ______________________________________                                    

EXAMPLE 14

This example illustrates the use of2,13-dimethyl-3,7,12,18-tetraazabicyclo-[12.3.1]octadeca-1,(18),2,8,12,14,16-pentaenecobalt (II) bromide as a catalytic chain transfer agent in the solutionpolymerisation of methyl methacrylate (MMA).

The title compound was prepared in an analogous manner to that for thepreparation of Co-pydiene from the reaction of diacetyl pyridine withspermidine (3-aminopropyl-3'-aminobutylamine) in the presence of cobalt(II) bromide. The general procedure for solution polymerisation wasfollowed using the indicated amount of the title compound and theresults were as shown below (molecular weights were measured after 1hour reaction time).

    ______________________________________                                        Example Solvent  [MMA]/[Co]   Mn    Mw/Mn                                     ______________________________________                                        14a     MeOH     100,000      18,620                                                                              2.40                                      14b     MeOH     50,000       11,700                                                                              2.26                                      14c     MeOH     10,000        8,306                                                                              2.05                                      ______________________________________                                    

A repeat of the above experiment with no catalyst gave a polymer withMn=55500, Mw/Mn=1.96.

EXAMPLE 15

This example illustrates the use of2,7,12-trimethyl-3,7,11,17-tetraazabicyclo-[11.3.1]heptadeca-1,(17),2,11,13,15-pentaenecobalt (II) bromide as a catalytic chain transfer agent in the solutionpolymerisation of methyl methacrylate (MMA).

The title compound was prepared in an analogous manner to that for thepreparation of Co-pydiene from the reaction of diacetyl pyridine with3,3'-diamino-N-methyl-dipropylamine in the presence of cobalt (II)bromide. The general procedure for solution polymerisation was followedusing the indicated amount of the title compound and the results were asshown below (molecular weights were measured after 1 hour reactiontime).

    ______________________________________                                        Example Solvent  [MMA]/[Co]   Mn    Mw/Mn                                     ______________________________________                                        15a     MeOH     100,000      16,080                                                                              3.54                                      15b     MeOH     50,000       14,980                                                                              3.11                                      15c     MeOH     10,000        7,373                                                                              2.56                                      ______________________________________                                    

A repeat of the above experiment with no catalyst gave a polymer withMn=43780, Mw/Mn=2.11.

EXAMPLE 16

This example illustrates the use of Co-pydiene as a catalytic chaintransfer agent in the emulsion polymerisation of methyl methacrylate (50wt %), methacrylic acid (30 wt %) and styrene (20 wt %).

The polymerisation apparatus consisted of a 2 litre baffled flangedflask fitted with a stirrer and condenser. The apparatus was evacuatedand flushed with nitrogen before use. The polymerisation temperature wasmonitorable using a thermocouple and digital read out. The reaction washeated using a thermostatically controlled water bath.

All monomers and water were degassed (deoxygenated) by passing a streamof nitrogen through them for at least one hour before use.

De-oxygenated, de-ionised water (758 ml) and sodium lauryl sulphate (8.4g) were charged to the reaction flask which was heated to 75° C. andstirred.

An aqueous solution of the cobalt catalyst was prepared. Co-pydiene(1.0592 g) was taken and added to a round bottomed flask. The flask wasevacuated and flushed with nitrogen three times. De-oxygenated,de-ionised water (100 g) was added via a syringe to the flask.

The monomer mixture was prepared in a round bottomed flask. The flaskwas evacuated and flushed with nitrogen three times. Styrene (88 ml),methacrylic acid (118.3 ml) and methyl methacrylate (213.7 ml) weretaken by syringe and added to the flask.

Cyanovaleric acid (5.1 g) and water (50 ml) were added to the reactionflask. The monomer mixture and aqueous solution of Co-pydiene were fedusing syringes attached to syringe pumps at a linear rate over a periodof 120 minutes. The temperature in the reaction flask was maintained at(75±2)° C. during the feed time and for a further 3 hours before coolingto ambient temperature.

The molecular weight of the resulting latex was determined by GPC andgave Mn 3053 and PDi 2.66.

What is claimed is:
 1. Process for the free-radical polymerisation ofolefinically unsaturated monomer(s) using a free-radical initiator,wherein said polymerisation is performed in the presence of a compoundfor effecting molecular weight control, said molecular weight controlcompound being selected from Cobalt II chelates of the followingformulae I, II and III: ##STR7## wherein: x and y are independently 2 to5;each R¹, R², R³ and R⁴ is independently selected from H, C1-C12 alkyl,optionally substituted aryl, OR⁵ where R⁵ is C1 to C12 alkyl oroptionally substituted aryl, CO₂ R⁵, SO₃ H, C(═O)R⁵, CO₂ H, NO₂, OH, NR⁵₂, NH₂, NHR⁵, SR⁵, SH, CN, SO₃ R⁵, halogen, 2-furyl and 3-furyl; each Xis independently selected from (CR⁶ ₂)_(n), (CR⁶ ₂ O)_(n), optionallysubstituted o-phenylene, and optionally substituted 1,8-naphthylene,where each R⁶ is independently selected from H and C1 to C12 alkyl, andn is 1 to 10; and wherein said cobalt chelates of formulae I and IIpossess a positive charge of 2 and are associated with an anion oranions for balancing the positive charge, while that of formula III isneutral; and also Co III analogues of said cobalt II chelates offormulae I, II and III in which the Co atom is additionally covalentlybonded, in a direction at right angles to the macrocyclic chelate ringsystem, to H, a halide ion or other anion, or a homolyticallydissociatable organic group.
 2. Process according to claim 1 wherein theanion associated with said cobalt chelates of formula I or formula II isselected from NO₃ ⁻, Cl⁻, Br⁻, N₃ ⁻, CN⁻, OH⁻, C₂ O₄ ⁻, I⁻, BF₄ ⁻, PF₆⁻, SbF₆ ⁻, ClO₄ ⁻, NCS⁻, R⁷ CO₂ ⁻ where R⁷ is C1 C8 alkyl, and SO₄ ²⁻.3. Process according to either claim 1 or claim 2 wherein each R¹ isindependently selected from H, C1-C12 alkyl and optionally substitutedphenyl; each R² is independently selected from H, C1-C12 alkyl andoptionally substituted phenyl; each R³ is independently selected from Hand C1-C12 alkyl; and R⁴ is selected from H and C1 to C12 alkyl. 4.Process according to any one of the preceding claims wherein each R¹ isindependently selected from H and CH₃ ; R² is H; each X is independentlyselected from (CH₂)₂ and o-phenylene, each R³ is independently selectedfrom H and CH₃ ; R⁴ is selected from H and CH₃, and x=y=2 or
 3. 5.Process according to claim 4 wherein there is used a cobalt chelatecomplex of formula I, and in which further each R¹ is CH₃, each R² is H,each R³ is H, x=y=3, and R⁴ is H.
 6. Process according to claim 5wherein the charge balancing anion is Br⁻, this cobalt chelate havingthe formula ##STR8##
 7. Process according to claim 4 wherein there isused a cobalt chelate complex of formula III, and in which further eachR¹ is H, each R² is H, the bottom X is CH₂ CH₂ and the top X iso-phenylene, this cobalt chelate having the formula ##STR9##
 8. Processaccording to any one of the preceding claims wherein said cobalt chelatehas a further ligand(s) coordinated to the cobalt atom which does notalter the cobalt valency state, said ligand being selected from weaklybasic tertiary amines, ethers, optionally substituted trialkyl, triaryl,or tri(alkyl/aryl)phosphines and the corresponding alkoxy or aryloxyphosphines, and water.
 9. Process according to any one of the precedingclaims wherein said polymerisation is a bulk or solution polymerisation.10. Process according to any one of claims 1 to 8 wherein saidpolymerisation is an aqueous suspension or aqueous emulsionpolymerisation.
 11. Process according to any one of the preceding claimswherein said process is applied to the homo- or copolymerisation ofmethacrylate esters or styrenes.
 12. Process according to any one ofclaims 1 to 10 wherein said monomer(s) polymerised is selected from atleast one or more of C1 to C10 alkyl methacrylates, C1 to C10 alkylacrylates, methacrylic acid, styrene and styrene derivatives. 13.Process according to any one of claims 1 to 10 wherein the monomerpolymerised is selected from at least methyl methacrylate, ethylmethacrylate, propyl methacrylate (all isomers), butyl methacrylate (allisomers); the corresponding acrylates; functionalised methacrylates andacrylates selected from glycidyl methacrylate, trimethoxysilyl propylmethacrylate, allyl methacrylate, hydroxyethyl methacrylate,hydroxypropyl methacrylate, and dialkylaminoalkyl methacrylates;fluoroalkyl (meth) acrylates; methacrylic acid, acrylic acid; fumaricacid (and esters), itaconic acid (and esters), and maleic anhydride;styrene, α-methyl styrene; vinyl chloride and vinyl fluoride;acrylonitrile, methacrylonitrile; vinylidene halides of formula CH₂═C(Hal)₂ where each halogen is independently C1 or F; optionallysubstituted butadienes of the formula CH₂ ═C(R⁸) C(R⁸)═CH₂ where R⁸ isindependently H, C1 to C10 alkyl, C1, or F; sulphonic acids orderivatives thereof of formula CH₂ ═CHSO₂ OM wherein M is Na, K, Li,N(R⁹)₄, R⁹, or --(CH₂)₂ --D where each R⁹ is independently H or C1 toC10 alkyl, D is CO₂ Z, OH, N(R⁹)₂ or SO₂ OZ and Z is H, Li, Na, K orN(R⁹)₄ ; acrylamide or derivatives thereof of formula CH₂ ═CHCON(R⁹)₂,and methacrylamide or derivates thereof of formula CH₂ ═C(CH₃)CON(R⁹)₂,and mixtures of such monomers.
 14. Process according to any of thepreceding claims wherein there is used a free radical yielding initiatorselected from 2,2'-azobis(isobutyronitrile), 2,2'-azobis-(2-methyl)butanenitrile, 4,4'-azobis(4-cyanovaleric acid),2-(t-butylazo)-2-cyanopropane,2,2'-azobis[2-methyl-N-(1,1)-bis(hydroxymethyl)-2-hydroxyethyl]propionamideand 2,2'-azobis[2-methyl-N-hydroxyethyl)]-propionamide.